1. Field of the Invention
One or more embodiments of the invention relates to an adaptation probe for insertion into implanted electrode devices of active medical implants to enable them for use in high-frequency magnetic alternating fields of MRI systems. Embodiments of the invention furthermore relate to a set composed of such an implantable electrode device and an adaptation probe that can be inserted therein.
2. Description of the Related Art
Regarding the background of the invention, it should be pointed out that the subject matter of one or more embodiments of the invention is relevant primarily in conjunction with cardiac pacemakers, implantable defibrillators, and other types of active implantable electromedical devices. The latter typically comprise at least one current/voltage-carrying supply lead in the electrode device—typically referred to simply as “electrode”—, the distal end of which is disposed e.g. in a ventricle and is used to measure cardiological potential signals or to transmit relevant therapeutic current signals.
The compatibility of such electrode devices in the case of implantable electromedical devices having high-frequency magnetic fields of the type used in imaging diagnostic methods in particular which are based on magnetic resonance—so-called MRI (magnetic resonance imaging) methods—is a serious problem. In the case of such MRI methods, a magnetic alternating field puled with radio frequency (RF) is superimposed on a strong static magnetic field, which is used to change the energy status of the protons in the tissue being investigated and to produce corresponding MRI signals from the tissue.
Due to the laws of electromagnetic induction, this magnetic alternating field induces alternative voltages in the supply lead of the electrode devices—under discussion here—of electromedical device implants, the energy of which is converted to heat at the electrically conductive contact poles, in particular, of the electrode device with human tissue. This can result in considerable heating e.g. of the tip contact of a cardiac electrode with corresponding impairment and even damage of the cardiac tissue in contact therewith or that surrounds it.
To prevent these problems, U.S. Pat. No. 7,363,090 B2 proposes the use of filters on the basis of oscillating circuits of parallel-connected coil and capacitor, which is assigned to the corresponding supply lead for the tip contact pole or a ring contact pole of a corresponding electrode of an implantable electromedical device. The filters disclosed in this known patent are designed—in practical application by the patent owner—as relatively voluminous components that reinforce the electrode device along a certain length and impart unfavorable mechanical properties to the electrode equipped therewith. Furthermore, the filter is accommodated in a closed housing that does not provide passage for the guide wires that are typically used when implanting an electrode. To this extent, the potential uses of this known electrode with filter devices is limited.
Document US 2009/0281592 A1 makes known filter components for reducing the heating of pacemaker electrodes of an electromedical implant due to the effect of high-frequency magnetic fields produced during MRI procedures, in which case an induction coil is installed around a non-conductive central section of a shank which connects a tip contact pole to an inner spiral conductor of the electrode device. By installing an induction coil on the shank, inductive signal filtering is achieved to reduce the electrode tip without the need for a relatively long, voluminous coil body along the length of the electrode. Capacitive elements can also be integrated in the shank to create an LC filter circuit. As an alternative thereto, a so-called “air coil” is disclosed in this publication as an inductive element, in the case of which the shank may be omitted.
A disadvantage of the prior art described is the fact that such electrode devices must be equipped individually, according to their design, with the appropriate circuits to implement a filter function at the production stage. Conventional electrode devices without such protective devices and, in particular, those that are already implanted in a patient without the appropriate filter devices pose a risk when introduced into a high-frequency magnetic field.